1. Field of the Invention
The present invention relates to a web cleaning and destaticizing apparatus for removing deposits such as fine dust, etc., deposited on a surface of a continuously running web. More particularly, the present invention relates to a web cleaning and destaticizing apparatus in which dust on a surface of the web is removed by a cleaning solution just before the coating composition is applied onto the surface of the web.
Incidentally, the terminology "web" used in the present invention generally includes a flexible belt-like member which has a width in a range of from 0.3 to 2 m, a length in a range of from 45 to 15,000 m and a thickness in a range of from 3 to 200 .mu.m, and which is formed of: plastic film made of such as polyethylene terephthalate, polyethylene-2, 6-naphthalate, cellulose diacetate, cellulose triacetate, cellulose acetate propionate, polyvinyl chloride, polyvinylidene chloride, polycarbonate, polyimide, polyamide, aramid, or the like; paper; paper applied or laminated with .alpha.-polyolefin having 2-10 carbons such as polyethylene, polypropylene, ethylene-butene copolymer, or the like; metal foil such as aluminum, copper, tin, or the like. The terminology "web" also includes a belt-like member which use an aforementioned belt-like member as a base material and have a finished layer formed on the surface of the member.
Further, the web is coated with a coating composition in accordance with the purpose of use. For example, a photographic light-sensitive coating composition, a magnetic coating composition, a surface protective coating composition, an antistatic coating composition, a lubricating coating composition, or the like is applied onto a surface of an original web. After being dried, the original web is cut into pieces each having a required width and a required length. Typical products of such webs may be photographic film, photographic printing paper, magnetic tape, magnetic disk, etc.
2. Description of the Related Art
As a conventionally well-known web dust removing apparatus, there are some types of apparatus. One is a doctor blade type disclosed in Japanese Patent Unexamined Publication No. Sho. 62-65872 as shown in FIG. 4. Another is a rotary-rod-bar-equipped extruder type as shown in FIG. 5. Before a dust removing process, a web cleaning solution SOL1, mainly containing an organic solvent, is applied onto one surface of a web W. In each type of web dust removing apparatus, the web cleaning solution SOL1 is removed by a doctor blade 2 in FIG. 4 or a rotary rod bar 12 in FIG. 5 at the upstream position of the running direction of the web. While the web cleaning solution SOL1 is removed, fine deposits on the one surface of the web W are also removed together with the web cleaning solution SOL1.
A conventional web dust removing apparatus 1, which is doctor blade type, is shown in FIG. 4. In the conventional doctor blade type, a doctor blade 2 is provided with a relatively small width and a relatively small radius of curvature R in a range of from about 2 to 30 mm. On the upstream side of the curved upper surface of the doctor blade 2, a cutting edge is provided. The web W coated with the web cleaning solution SOL1 is guided to run in the direction of the arrow A, and a web incident angle .alpha. is formed in a range of from about 0.5.degree. to 2.degree. where the web W and a tangential line of the cutting edge cross. Then, fine deposits DP on one surface of the web W are scraped off together with a part of the web cleaning solution SOL1 applied onto the web. After being collected into a solution collection groove 3, which is disposed below the doctor blade 2, the web cleaning solution SOL1 is discharged to a cleaning solution recycle system (not shown).
On the other hand, a FIG. 5 shows a web dust removing apparatus 10, which is a conventional rotary-rod-bar-equipped extruder type. In the conventional rotary-rod-bar-equipped extruder type, a rotary rod bar 12 is provided above a block on the upstream side, which forms a slit 15 communicated with a pocket 14 provided, by holing, in the inside of an extruder 11. The rotary rod bar 12 is rotatable in a direction B reverse to the running direction A of the web W. Then, fine deposits DP on one surface of the web W are scraped off together with a part of the web cleaning solution SOL1 by the outer circumferential surface of the rotary rod bar 12. After being collected into a solution collection groove 3 disposed at a lower portion of the extruder 11, the web cleaning solution SOL1 is discharged into a cleaning solution recycle system (not shown).
Further, in the conventional web dust removing apparatus 10 of rotary-rod-bar-equipped extruder type, electrostatic charges after the scraping can be suppressed, while the electrostatic charges are expected in the conventional web dust removing apparatus 1 of doctor-blade type. In order to suppress the electrostatic charges, the following design is employed. First, an undercoat solution (SOL2) is supplied to a pocket 14. The undercoat solution (SOL2) contains compositions equivalent to those of the web cleaning solution SOL1 or contains additives in a solvent of the same kind as that of the cleaning solution (SOL1). Second, a back edge 16 is provided on a upper surface of the block of the downstream side and forms a slit 15. Then, the undercoat solution (SOL2) is introduced through the slit 15 and into the space between the back edge 16 and the web W, which has passed the rotary rod bar 12. After being introduced, the undercoat solution (SOL2) is applied onto the surface of the web W to thereby attain destaticization.
However, in the conventional web dust removing apparatus 1 of doctor blade type, the running speed of the web W can be increased in order to improve dust-removing effect. increasing the improvement in the dust-removing effect results in a greater quantity of the web cleaning solution SOL1 to be scraped off. This means the curved upper surface of the doctor blade 2 is arranged to the place which is more closer to the one surface of the web W. The above-described increment of the speed and arrangement of the doctor blade 2 result in the cleaning solution SOL1 scattering in the surrounding directions easily, and a strong shear force acts on the web W. By this strong shear force, the web W passing the doctor blade 2 is electrostatically charged abnormally large amount. As a result, there was a fear that it would cause a problem by attracting and absorbing floating dust, or the like.
Further, in the conventional web dust removing apparatus 10 of rotary-rod-bar-equipped extruder type, the running speed of the web W and the quantity of the web cleaning solution SOL1 to be scraped off can be increased so as to improve dust-removing effect. However, as in the case of the conventional web dust removing apparatus 1 of doctor blade type, the increment of the speed and the increment of the quantity result in the cleaning solution SOL1 scattering in the surrounding directions easily. As a result, the scattered solution deposits on the surface of the web W again, and lowers the dust-removing effect. Furthermore, this might cause a trouble of lowering the quality in the coating surface because of pinholes, or the like.
Further, in each of the conventional web dust removing apparatus 1 and 10, incidental equipment are complicated and expensive in order to accurately set the web incident angle .alpha. of the web W with respect to the doctor blade 2 or the rotary rod bar 12, the quantity of application of the web cleaning solution SOL1, etc. If all those settings are done mainly by human hand, human setting errors might cause an abnormal increase of electrostatic charges.